This invention relates to a method for conserving a resource by interrupting the flow of the resource. More specifically, it relates to a method for reducing water consumption by a semiconductor wafer grinding machine during a non-processing idle mode.
Moderm manufacturing equipment relies on various resource or facility inputs in order to operate. For example, electricity is directly or indirectly required to run most, if not all such machinery. In addition, many machine processes require additional facilities such as compressed gas or air, vacuum pressure, and chemical, hydraulic, and aqueous flow to name a few. These facilities are the direct or indirect product of conventional expendable resources (e.g., electricity, gas, water). Accordingly, it is economically and environmentally advantageous to conserve or minimize usage of these facilities. While the present invention is applicable to conserving most any facility, it is primarily directed to conservation of liquid flow and, more particularly, water flow to a semiconductor wafer grinding machine. The remainder of this discussion will focus on the same.
In conventional wafer grinding, a wafer having a front side covered with a protective layer is placed on a vacuum chuck. The back side of the wafer is then brought into contact with a grinding wheel. As the grinding wheel passes over the wafer, it removes a thin layer of wafer material. Due to the frictional engagement of the grinding wheel with the wafer, heat is produced. To cool the wafer and the surrounding tool surfaces, a liquid coolant system is typically included. The coolant system provides directed flow of municipal or de-ionized water over the various components including the wafer and grinding wheel, thus maintaining a consistent temperature. In addition to cooling, the coolant rinses away the wafer material removed by the grinding wheel.
To monitor the amount of material removed from the wafer, the grinding machine also includes sensors or transducers that constantly monitor wafer thickness. It is critical that these sensors deliver accurate data throughout the grinding operation. Unfortunately, the output from these transducers is highly influenced by changes in temperature. To ensure accurate and repeatable data, the sensors are calibrated and operated within a narrow temperature range. Outside that range, sensor accuracy becomes unreliable. Accordingly, it is important to maintain the wafer thickness sensors at a consistent temperature throughout the grinding process.
During operation, the grinder typically grinds wafers continuously for a period of time. When grinding is complete, the machine enters a non-operational or xe2x80x9cidle modexe2x80x9d at which time no wafer processing is occurring.
To conserve water, the coolant water flow may be shut off during idle mode. Unfortunately, when water flow is discontinued, the temperature of the sensors (and the other tool surfaces) changes. As discussed above, temperature variation has an adverse effect on sensor accuracy. Furthermore, the time required to bring the grinder back to operating temperature once water flow is restored may be extensive due to the size and mass of the machine.
Another problem with discontinuing the water supply to the grinder is that waste material not yet removed at the completion of the grinding operation may still be present. That is, material removed from the last processed wafers may not be completely rinsed from the grinding station at the time it enters idle mode.
To preserve sensor accuracy, eliminate xe2x80x9cwarm-upxe2x80x9d time, and keep the grinder clean, some grinders apply a continuous water spray even during idle mode. While this assures consistent temperature and improves cleanliness, it also wastes a significant amount of water.
Thus, there are unresolved issues with current wafer grinding techniques. What is needed is a method of conserving water supplied to the grinder during idle mode that will not adversely affect the temperature of the various grinding surfaces and components. What is further needed is a method that will adequately purge the grinder of any waste material whenever the grinder enters idle mode.
A method and system for conserving a facility delivered to a device are described herein. The method, in one embodiment, comprises providing facility delivery means and delivering the facility to the device through the facility delivery means. In addition, control means are provided between the facility delivery means and the device to allow adjusting the rate of delivery of the facility. The facility is delivered at a first rate of delivery when the device is in an active mode and at a second rate of delivery when the device is in an idle mode.
A system for controlling delivery of water to a machine is also disclosed. In one embodiment, the system comprises a water delivery conduit; a flow control valve within the water delivery conduit; and a valve controller coupled to the flow control valve. The valve controller is adapted to monitor the machine to determine whether the machine is in an active mode or an idle mode. The valve controller can manipulate the flow control valve to deliver water at a first flow rate during active mode and at a second, reduced flow rate during idle mode.
In yet another embodiment, a method for conserving a facility delivered to a machine is described comprising providing a facility delivery device and delivering the facility to the machine through the facility delivery device. The method further includes providing control means between the facility delivery device and the machine. By adjusting the rate of delivery of the facility with the control means, the facility is delivered at a first rate of delivery when the machine is in an active mode and at a second, reduced rate of delivery when the machine is in an idle mode. The delivery of the facility may be modulated when the machine is in idle mode such that the control means intermittently increases the rate of delivery of the facility to a level higher than the second rate of delivery.
In still yet another embodiment, a grinder used during semiconductor fabrication is disclosed. The grinder comprises: a wafer chuck adapted to support a wafer; a grinding wheel proximal the wafer chuck; one or more sensors to monitor the wafer thickness; and a machine controller to monitor and control grinding operations. The grinder further includes a coolant system adapted to provide coolant to the grinder. The coolant system includes a coolant delivery conduit; a flow control valve within the coolant delivery conduit; and a valve controller coupled to the flow control valve. The valve controller is adapted to monitor the grinder to determine whether the grinder is in an active mode or an idle mode, wherein the valve controller can manipulate the flow control valve to reduce coolant flow when the grinder enters idle mode.
Advantageously, the present invention can effectively reduce consumption of a facility provided to equipment which periodically enters a non-operational idle mode. By monitoring the status of the equipment, the delivery of the facility may be reduced or terminated when the equipment enters idle mode. To maintain the operational readiness of the machine and eliminate the need for a subsequent xe2x80x9cwarm-upxe2x80x9d period, the delivery of the facility may be periodically restored or increased during idle mode. In addition, a delay may be provided so that elevated delivery of the facility is maintained momentarily after entering idle mode. Accordingly, the present invention permits facility conservation during idle mode without the undesirable consequences that may result from total facility termination.